Late Middle English applicacioun, from Old French aplicacion (French application), from Latinapplicātiōnem, accusative singular of applicātiō (“attachment; application, inclination”), from applicō (“join to, attach; apply”).

application - Computer Definition

A program designed to perform a function or suite of related functions of benefit to an end user, with examples being accounting, mathematical analysis, video editing, and word processing. Application software differs from utilities, which are devoted to system management tasks. See also utility.

(1) Software that is used for business or entertainment. The terms "application," "application program," "software application" and simply "app" may refer to virtually any type of program from spreadsheets such as Excel to media players such as iTunes to virtual reality games such as Second Life. However, the term specifically excludes essential control software such as the operating system (see system software).
One or Many Files
In the computer, an application can be made up of a single executable file or hundreds of files, which includes additional software modules, configuration files and ancillary data files. See application program and application software.

(2) A particular purpose for using technology such as a computer. An application can refer to a functional category such as payroll, inventory and billing, or to a business category such as manufacturing, banking or retail. It may also refer to scientific or medical categories. Although awkward, one could use the word to mean both definitions #1 and #2 in the same sentence. For example, "this application is used in medical applications" is technically correct.